Liquid level gauge



April 8, 1947. D. H. ANNIN LIQUID LEVEL GA UGE Filed March 6, 1944- file Patented Apr. 8, 1947 UNITED sTA'rEs PATENT OFFICE v p 2,418,614 LIQUID LEVEL GAUGE Douglas H. Annin, Oakland, cane, assignor, by

mesne assignments, to Fluid Control Engineer ing 00., Emeryville, Calif., a copartnership consisting of M. H. Grove and J. E. Grove, both of Piedmont, Calif.

Application March 6, 1944, Serial No. 525,169

' 4 Claims. (01. 73-302) This invention relates generally to gauges or indicators such as are employed for indicating the. depth of liquid in various tanks or storage vessels.

. It is a general object of the invention to provide a liquid level gauge of the pneumatic type,

which will give greater accuracy than devices 01" ferred embodiment has been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing: Fig. 1 is a side elevational view illustrating equipment incorporating the present invention.

Fig. 2 is an enlarged side elevational view in section, showing the bleed valve and associated parts incorporated in the equipment of Fig, 1.

Fig. 3 is a cross-sectional detail, on an enlarged scale, showing the construction of the manually operated valve incorporated in the equipment of Fig. 1.

In the past liquid level gauges of the pneumatic type have been constructed with adiaphragm operated bleed or pilot valve, in conjunction with an air gauge and a source of air supply. The source of air is connected through a flow restricting orifice to piping leading to the bleedvalve and to the gauge. At the bleed valve the air pressure in the pipin is applied to one side of the diaphragm, while the other side of the diaphragm is directly exposed to liquid in the tank, as by mounting the diaphragm in a side wall of the tank near the bottom of the same.

With such equipment the pressure in the piping connecting the gauge to the bleed valve is determined by the liquid pressure applied to the diaphragm, and therefore the indicated gauge pressure is a direct function of the liquid level. Such equipment general] lacks accuracy because the pneumatic pressure applied to the diaphragm must be comparable to the liquid pressure from the tank, and this necessitates use of, a special low pressure gauge. Surges of the liquid in the tank also cause flexing of the diaphragm, with plied to the gauge.

resulting undesired variations in the pressure ap- The present invention likewise makes use of'a bleed valve operated in accordance with the level of liquidin the tank. This bleed valve is likewise connected, by piping to a pressure gauge, and the piping is supplied with air from a source of supply, through an orifice. However, as will be presently described the pneumatic pressure is not applied directly to the diaphragm, and a damping action is introduced which serves to eliminate rapid movements of the diaphragm.

As the equipment is illustrated in the drawing (Fig. 1) it consists of a unit A which incorporates a bleed valve and associated fiuid pressure operated members. Thi unit is connected by pipe ID to the tank of the pipe extends to or near the central axis of the tank in the lower portion of the same, as indicated at II. Piping I2 also connects unit A with the control unit C, which can be conven iently mounted on a panel l3. This panel carries the pressure gauge M, the readings of which show the level of liquid within the tank. Device C also connects with the air supply pipe l6, leading to a suitable source of air under pressure.

Unit A as illustrated in Fig. 2 consists of. a

suitable hollow body H, which is annular in transverse cross-section, and which forms a mounting for the flexible diaphragm I 8. The peripheral edge portion of the diaphragm I8 is shown clamped between the annular ring [9, and the circularly contoured closure plate 2|. Ring I9 is carried upon the flange 22, formed on the body I1. Closure plate 2| together with diaphragm I8 forms a closed external chamber 23 which connects with the pipe Ill.

The other side of the flexible diaphragm I8, that is the lower side as seen in Fig.2, operatively connects with a pressure cell 24, and this cell in turn is associated with a second pressure cell 26. Both of these cells can be metal bellows of the Sylphon type, as illustrated. To form an operative connection between cell 24 and the diaphragm l8, the upper end of this cell is shown attached to, the end wall 21, and this wall has a circular rim or flange 28, which surrounds the annular rib 29 formed upon the lower side of the diaphragm thrust plate 3|.

The lower end of the cell 24 is secured and sealed with respect to a transverse wall 32; The peripheral edge portion of this wall is clamped to the body between the" lower end of sleeve 33, and the annular shoulder 34.

sleeve 33 engages the lower side of ring l9.

B. Preferably the open end The upper end of aeiaers Theupper end of the 'cell 26lsllkewlsesecured to and sealed with' respect to wall 32, and the lower end of this cell is secured to and sealed with respect to the end wall 36. The interiors of the cells 24 and 26 are completely filled with a suitable liquid, such as glycerine or a mineral oil, and they are interconnected by the relatively small flow restricting orifice 31.

The bleed or pilot valve means consists of the stationary and movable valve members 33 and 33.- Valve member 36 is shown as a circular or annular knife edge 4|, surrounding the outflow or vent passage 42, and formed upon the inner end of the removable screw.43. Valve member 36 can be a simple insert formed suitable composition ,or synthetic rubber and retained upon the lower side of the end wall, 36. In full closed 26 is connected to the pipe l2, whereby the exterior o1 the'cell '26 is exposed to the pressure oi. air existing in the piping i2. The space 46 surrounding the cell 24 is connected to the atmosphere through the port 5i.

With the cells 24 and 26 filled with liquid as described above, it is evident that flexing of diaphragm It in one direction, such as downwardly as viewed in Fig. 2, to compress'the cell 24, causes displacement of liquid from this cell through a restricted orifice 31 to expand the cell 26. Likewise air pressure in chamber 46 tends to compress the cell 26, and any such compression expels liquid from this cell through orifice 31 to expand the cell 24. .The effective area. of the cell 26 which is exposed to air pressure in chamber 46 is preferably substantially less than the effective pressure area of the diaphragm l8. The efiective fluid area of the diaphragm is preferably determined by a pair of rings or washers 53 and 54, which engage the sides of the diaphragm, and which definitely limit the area of the diaphragm subject to flexing, By changing the dimensions of the rings 53 and'54, the ratio between I ,4 the pressure of this liquid is transmitted through pipe It to the diaphragm l6. Because the diaphragm is flexible it in turn transmits iorce to 1 the cell 24 in a direction to compress the same.

Liquid in cell 241s therefore placed under pressure and this pressure is transmitted through orifice 31, to the liquid in .cell 26. Assuming a static liquid level and that button 65 is depressed, the liquid pressure within cell 26 is exactly balanced by the pneumatic pressure in chamber 46. At the same time there is-continuous bleeding oi! of air from chamber 46, through the valve pas-' sage 42.- The bleed of! is such as to maintain the pressure in chamber 46 constant. The pneumatic pressure in chamber 46 is indicated by the reading of gauge l4, and this reading is therefore an indication or'measurement of the depth oi liquid in tank B.

Assuming that there is an increase in the depth of liquid in tank B, the pressure-upon diaphragm I6 is increased whereby a slight collapsing of cell 24- causes flow of liquid through orifice 31, to slightly expand cell 26. This in turn either closes or partially closes valve member 39 upon seat 4|,

thus permitting a building up of pressure in cell 46, The build up continues until equilibrium is again established, at which time the gauge l4 again indicates the liquid level. Actually unless the liquid level in tank B is increased very rapidly, the buildup of pressure in chamber 46 takes place simultaneously and at about the same rate as the increase in the liquid level, so that there is no lag in the reestablishment of equilibrium.

The device 0 shown in Fig, 3 can consist of a I body 56 having passages '51 and 58, which connect with the pipes 12 and i6. Passage 51 also connects with the pipe 59, leading to the pressure gauge l4. Communication between passages 51 and 58 is controlled by a small manually, operated push valve. This valve-can consist for example of a stationary valve seat 6i, formed within the body, and cooperating-with the movable valve member 62, which in turn is carried by the operating rod 63. A compression spring 64 urges valve member 62 upon the seat and the rod 63 is provided withabutton 65.

A fiow restricting orifice 66 is formed in the body 56 and serves to restrict flow of air from the source of pressure. This orifice may be varied as to size to suit varying installation conditions. The source of air to which pipe l6 connects should be maintained at-a relatively constant pressure, and at a pressurelevel well above the pressure in pipe l2 for maximum reading of the gauge l4.

The apparatus described above operates as follows: Assuming a quantity of liquid in tank B,

A drop in liquid level in tank B causes a dropin pressure upon diaphragm l6, and this in turn conversely causes a-slight expansion of cell 24 with flow through orifice 31 in a. reverse direction, to slightly contract the cell 26. This in turn causes movement of the valve member 39 away from its seat to vent the air from chamber 46 at an increased rate until equilibrium is again tablished.

Instead of having pipes I6 and I2 continuously connected, as when the manual button 66 is continuously depressed,-it is desirable to have this valve normally closed, and to simply depress the same manually to secure a reading of the gauge I4. The operation in such event is the same as previously described, except that equilibrium to secure proper reading of gauge I4 is quickly established, in each instance, when the button 65 is depressed.

Assuming that, the diaphragm i6 has an effective fluid area considerably greater than that of the cell 26, it is apparent that the pressures in chamber 48 to establish equilibrium are substantially greater than the pressure which would be required if applied directly to the underside of diaphragm l6. Therefore for the average type of liquid tank it is not necessary to use special low pressure gauges, but standard gauges adapted for greater pressures can be employed with a high degree of accuracy, Such gauges can be calibrated to directly read in terms of depth of liquid,

, ject to movement, as on hips.

Because the diphragm I6 is located outside the the orifice, a diaphragm forming a, fixed fluid 1 pressure area, means for applying liquid pressure from the lower portion of the tank toone side of the diaphragm, a compressible cell operatively connected to the diaphragm and adapted to be compressed or expanded reponsive to flexing movements of the diaphragm, a second compressible cell affording a flxed fluid pressure area and connected to the movable member of the bleed valve, both said cells being filled with liquid and being connected together through a flow restricting orifice, and means for applying pneumatic pressure from the outflow side of the first mentioned orifice to the fluid pressure area of the last named cell.

2. In a liquid level gauge, a bleed valve comprising stationary and movable valve members, a source of gas under pressure connected to the bleed valve through a restricted orifice, a pressure gauge also connected to the outflow side of the orifice, a diaphragm forming a fixed fluid pressure area, means for applying liquid pressure from the lower portion of the tank to one side of said diaphragm, a Sylphon tube operatively connected to the diaphragm and adapted to be compressed or expanded responsive to flexing movements of the diaphragm, a second Sylphon tube connected to the movable valve member of the bleed valve, both said Sylphon tubes being fllled with liquid and the two tubes being connected by a flow restricting orifice, the second Sylphon tube affording a fluid pressure area differing from the fluid pressure area presented by the diaphragm, and means for applymg fluid pressure from the outlet side of the first named restricted orifice to the pressure area presented by the second Sylphon tube.

3. In a liquid level responsive apparatus for tanks and of the type utilizing a bleed valve, a source of gas under pressure connected to the bleed valve through a restricted orifice and a pressure responsive device also connected to the outflow side of the orifice; a pressure responsive control unit comprising a diaphragm forming a fixed fluid pressure area, means forming a fluid chamber on one side of the diaphragm adapted to be connected to the lower portion of the tank, a compression cell operably connected to the diaphragm and adapted to be compressed or expanded responsive to flexing movements of the diaphragm, a, second compressible cell aflording a fixed fluid pressure area, a bleed valve comprising stationary and movable valve members, a connection between the second cell and the movable bleed valve member, both said cells bein filled with liquid and being connected together through a flow restricting orifice, and means forming a fluid pressure chamber about said last named cell adapted for fluid connection to a source of pneumatic pressure.

4. In a liquid level gauge for tanks and of the type using a bleed valve, a source of gas under pressure connected to the bleed valve through a restricted orifice. and a pressure gauge also connected to the outflow side of the orifice and adapted to indicate the level of liquid in the tank; a pressure responsive control unit comprising a diaphragm forming a fixed fluid pressure area, means forming a liquid chamber on one side of the diaphragm and adapted for connection to the lower portion of the tank, a Sylphon tube operatively connected to the diaphragm and adapted to be compressed or expanded responsive to flexing movements of the diaphragm, a second Sylphon tube, a bleed valve comprising stationary and movable valve members, a connection between the movable bleed 'valve member and the second Sylphon tube, both said Sylphon tubes being fllled with liquid and the two tubes being connected by a flow restricting orifice, the second Sylphon tube affording a fluid pressure area differing from the fluid pressure area presented by the diaphragm, and means forming a fluid chamber aboutlsaid last named Sylphon tube adapted to be connected to the aforesaid outflow side-of said first named orifice.

40 DOUGLAS H. ANNIN.

REFERENCES CITED The following references are oi. record in the flle of this patent: UNITED STATES PATENTS Number Name Date 2,312,201 Thompson et a1 Feb. 23, 1943 2,265,114 Hartley Dec. 2, 1941 1,631,909 Badin June 7, 1927 1,805,802 Browne May 19, 1931 2,140,954 Frazee Dec. 20, 1938 FOREIGN PATENTS I Number Country Date 375,979 Italian Oct. 26, 1939 

